Studies will be extended on synthetic analogs of the neurohypophysial peptides aimed at further definition of structural changes that lead to enhanced activities and specificities as agonists and antagonists. Antagonistic peptides will be used as pharmacological tools to investigate the physiological functions of endogenous neurohypophysial hormones. The mode of action of natriuretic peptides on the kidney will be explored as well as the means by which opiates influence the release of neurohypophysial hormones. BIBLIOGRAPHIC REFERENCES: Lowbridge, J., M. Manning, J. Haldar and W.H. Sawyer (1977). Synthesis and some pharmacological properties of (4-threonine, 7-glycine)-oxytocin, (1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine, 7-glycine)-oxytocin (hydroxy(Thr4, Gly7)-oxytocin, and (7-glycine)-oxytocin; peptides with high oxytocic/antidiuretic selectivity. J. Med. Chem. 20:120-123. Manning, M., J. Lowbridge, J. Haldar and W.H. Sawyer (1977). Design of neurohypophysial peptides which exhibit selective agonistic and antagonistic properties. Fed. Proc. 36:1848-1852.